Scientists have put a price tag on the cost of high-tide floods on the coastal community of Annapolis, Md. High-tide floods, also called nuisance or sunny day floods, are small-scale inundations that last a few hours and flood areas with tens of centimeters of water during high tides. Rising sea levels are making high-tide floods more common: the Annapolis district of City Dock had 44 high-tide floods in 2017 alone.

“High-tide flooding is already measurably disrupting the economic activity in this location.”A study published today in Science Advances quantified the decrease in visits and the loss of revenue to downtown businesses due to 1 year of high-tide floods. The total parking lot visits to the downtown Annapolis district of City Dock decreased by about 3,000 in 2017 because of the floods. Miyuki Hino, the lead author and a doctoral student at Stanford University, said in a media briefing Thursday that “high-tide flooding is already measurably disrupting the economic activity in this location.”

The researchers also projected losses that rising seas could bring to the community. “With just three more inches [7.6 centimeters] of additional sea level rise,” Hino noted, “loss of visits would double.” The authors predict this will happen in the next 2 decades at the present rate of sea level rise.

Floods Scare Away Shoppers

Many towns around the United States may face challenges similar to Annapolis. A recent report found that more than 170 coastal communities will face flooding as frequently as 26 times per year by 2035. Small floods disrupt daily life by blocking streets, closing schools, and damaging vehicles.

The latest study calculated the impact of high-tide floods by tracking the dip in parking ticket sales in the downtown district of City Dock. The researchers created their own tally of high-tide floods using social media posts, police footage, and tidal gauges. The floods are often so ephemeral that no record was previously available.

The lack of customers translated to “about a hundred thousand dollars in lost revenue.”“We found that high-tide flooding reduced visits to City Dock by about 2%,” Hino explained. The depression in visits lasted after the flood subsided, even up to 5 hours after the flood occurred. The lack of customers translated to “about a hundred thousand dollars in lost revenue across about 16 businesses” in 2017, Hino said.

The study’s analysis does not take into account missed work days, delayed travel times, or damage to infrastructure. Although the authors note that the 2017 losses are small, their projections of future sea level rise suggest that City Dock could lose more than 37,000 visitors with just a 1-foot (0.3-meter) increase in sea level rise.

Local government officials in Annapolis are actively seeking grants to mitigate the issue, according to the study’s authors. The funds would go to build pumps to siphon away water from downtown. As the city faces more extreme floods due to sea level rise, “there are a range of adaptation options,” said coauthor Samanthe Tiver Belanger, a Stanford University business school graduate student.

“Some of them are as extreme as picking up the businesses and moving them entirely, whereas others are smaller,” she added, such as building walls.

Not Simply a Nuisance

Benjamin Hamlington, a scientist in the Sea Level and Ice Group at NASA’s Jet Propulsion Laboratory, told Eos that the latest study is “one of the first assessments of the effect of high-tide flooding on economic activity.”

“With increasing sea levels, it no longer takes a hurricane or strong storm to cause coastal flooding.”“One of the most important results is that high-tide flooding is already having a measurable impact on coastal populations, beyond simply being a nuisance,” Hamlington noted. “With increasing sea levels, it no longer takes a hurricane or strong storm to cause coastal flooding.”

Thomas Wahl, an assistant professor in coastal engineering at the University of Central Florida, told Eos that coastal planning often focuses on extreme events like hurricanes but misses the “cumulative effects” of small repeated floods. The paper raises a “very important emerging issue,” Wahl noted.

For study coauthor Chris Field, director of the Stanford Woods Institute for the Environment in Stanford, Calif., the latest findings are an example of how humans’ relationship to the coast is shifting.

“Many coastal areas in the U.S. are built as close to sea level as possible to facilitate the interaction between humans and the ocean,” Fields said. “But as the sea has risen, that closeness to the ocean has transitioned from being an asset to being potentially a liability.”

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